To minimize the electric energy loss during the course of power transmission via power lines, all the electrical grids over the world transmit electricity in the form of high-voltage alternating current (AC), which is stepped down at a substation near the consumers to a required working voltage for general domestic electrical appliances. Therefore, electrical networks for city and rural areas use AC power receptacles as their terminals.
In the past decades of years, technological development is so rapid that various types of digitalized electronic products, such as computers and communication apparatus, have been introduced into market and people's daily life. These digitalized electronic products are constantly personalized and miniaturized, and usually use the small-volume and rechargeable direct current (DC) battery as their power supply, so that the electronic products have further miniaturized dimensions and reduced weight and can be conveniently portable.
The above-mentioned personalized electronic products could not be directly powered or charged via the AC power receptacles that currently form the terminals of the electrical grids. Before the AC power supplied via the power lines can be supplied to power or charge a DC device, the AC power must be rectified, stepped down and stabilized via a rectifier to convert into DC power. However, since various types of electronic products respectively require a specific DC voltage, consumers must prepare many rectifiers of different voltages for different electronic products. This is of course very inconvenient to consumers.
One solution to this problem is to install a rectifying and transforming circuit in an electrical receptacle for converting the AC power supplied via the power lines into DC power and then outputting the converted DC power for use. To avoid waste of energy possibly caused by turning on the rectifying and transforming circuit over a long period of time, the electrical receptacle installed with the rectifying and transforming circuit is usually provided on a cover plate thereof with a control switch. When this type of electrical receptacle is mounted in an outdoor environment or a wet environment, such as in a kitchen or in a bathroom, water would invade into the electrical receptacle via gaps between the control switch and the cover plate to corrode the control switch as well as the rectifying and transforming circuit in the receptacle. In view of this shortcoming, it is necessary to improve the existing electrical receptacle that supplies DC power.